1. Field of the Invention
This invention relates to a method for making an insulating film particularly suitable for use in making an inter-layer insulating film in a semiconductor device.
2. Description of the Related Art
In a process of manufacturing a semiconductor device, a method for making an inter-layer insulating film using a fluid source material is often used to level the surface of a substrate by smoothing unevenness made by wiring or the like. Such an inter-layer insulating film contains much moisture (H2O) and is highly fluid.
In conventional techniques, a non-fluid cap layer was formed directly on a fluid inter-layer insulating film containing much H2O by plasma CVD (for example, 1995 Dry Process Symposium, pp.261-268) to prevent cracks in the fluid inter-layer insulating film containing H2O during post-annealing. Typically used as the cap layer was a SiO2 film made of SiH4 and N2O by plasma CVD because N2O was more preferable than O2 as the source material of oxygen in reducing the number of particles produced during the process.
However, the SiO2 cap layer made of SiH4 and N2O by plasma CVD invited corrosion of the metal wiring and created so-called poisoned via (a kind of defects of via holes (connection holes) formed in the inter-layer insulating films), among others.
It is therefore an object of the invention to provide a method for making an insulating film free from problems such as corrosion of metal wiring and poisoned via even when a fluid source material is used to make the insulating film.
The Inventor made researches to overcome the above-mentioned problems involved in the conventional techniques as summarized below.
The Inventor has found through various experiments that NH3 is produced in vapor by plasma in the process of making a SiO2 film by plasma CVD using SiH4 and N2O as source materials. Under the condition, if the inter-layer insulating film underlying the SiO2 film contains H2O and has a fluidity, then NH3 produced in the vapor is incorporated (absorbed) into the underlying inter-layer insulating film. NH3 incorporated into the underlying inter-layer insulating film is released from the film when the inter-layer insulating film is heated or etched in a later process, and probably cause the problems of corrosion of metal wiring and the poisoned via.
Therefore, in order to prevent these problems, it is important to take measures to prevent the NH3 which is produced in the vapor in the process of making the SiO2 film by plasma CVD using SiH4 and N2O as the source materials from being incorporated in the underlying inter-layer insulating film. For this purpose, it is effective to remove H2O from the surface of the underlying inter-layer insulating film and to cure the surface prior to the process of making the SiO2 film. The present invention has been made through these researches by the Inventor.
According to a first aspect of the invention, there is provided a method for making an insulating film configured to form the insulating film on a substrate having an uneven surface by using a fluid source material so as to level the unevenness, comprising the steps of:
forming a first insulating film having a fluidity on the substrate by using a fluid source material;
applying plasma processing onto the first insulating film; and
forming a second insulating not having a fluidity on the first insulating film after the plasma processing.
According to a second aspect of the invention, there is provided a method for making an insulating film configured to form the insulating film on a substrate having an uneven surface by using a fluid source material so as to level the unevenness, comprising the steps of:
forming a first insulating film having a fluidity on the substrate by using a fluid source material;
applying rapid thermal annealing by lamp heating onto the first insulating film; and
forming a second insulating not having a fluidity on the first insulating film after the rapid thermal annealing.
According to a third aspect of the invention, there is provided a method for making an insulating film configured to form the insulating film on a substrate having an uneven surface by using a fluid source material so as to level the unevenness, comprising the steps of:
forming a first insulating film having a fluidity on the substrate by using a fluid source material;
applying ozone processing onto the first insulating film; and
forming a second insulating not having a fluidity on the first insulating film after the ozone processing.
In the first aspect of the invention, the step of annealing the structure may be added after making the first insulating film and prior to plasma processing to previously cure the entirety of the first insulating film to a certain extent in order to ensure that the first insulating film be more effectively cured by subsequent plasma processing. The annealing temperature is not higher than 500xc2x0 C., and is about 350xc2x0 C., for example, when Al alloy wiring is used. The annealing may be done either under a vacuum or atmospheric pressure, but can be done more conveniently within a chamber used for the plasma processing. For plasma processing, it is preferable to use a gas of molecules, such as O2 gas, containing oxygen as its matrix atoms and not containing nitrogen as its matrix atoms.
In the present invention, the first insulating film having a fluidity is typically made by low pressure CVD using SiH4 or organosilane and H2O2 as the source materials.
According to the invention, having the above-summarized construction configured to execute plasma processing, rapid thermal annealing by using lamp heating or ozone processing after making a first insulating film having a fluidity, H2O can be removed from the surface of the first insulating film due to dehydrated condensation, and the film can be hardened. Therefore, even when NH3 is produced in the vapor by plasma while a SiO2 film is stacked on the first insulating film by plasma CVD using SiH4 and N2O as the source material gases, NH3 can be prevented from being incorporated into the first insulating film. As a result, corrosion of metal wiring or the problem of poisoned via can be prevented.
The above, and other, objects, features and advantage of the present invention will become readily apparent from the following detailed description thereof which is to be read in connection with the accompanying drawings.